Changes in temperature and precipitation extremes in the IPCC ensemble of global coupled model simulations

Temperature and precipitation extremes and their potential future changes are evaluated in an ensemble of global coupled climate models participating in the Intergovernmental Panel on Climate Change (IPCC) diagnostic exercise for the Fourth Assessment Report (AR4). Climate extremes are expressed in terms of 20-yr return values of annual extremes of near-surface temperature and 24-h precipitation amounts. The simulated changes in extremes are documented for years 2046–65 and 2081–2100 relative to 1981–2000 in experiments with the Special Report on Emissions Scenarios (SRES) B1, A1B, and A2 emission scenarios. Overall, the climate models simulate present-day warm extremes reasonably well on the global scale, as compared to estimates from reanalyses. The model discrepancies in simulating cold extremes are generally larger than those for warm extremes, especially in sea ice–covered areas. Simulated present-day precipita-tion extremes are plausible in the extratropics, but uncertainties in extreme precipitation in the Tropics are very large, both in the models and the available observationally based datasets. Changes in warm extremes generally follow changes in the mean summertime temperature. Cold ex-tremes warm faster than warm extremes by about 30%–40%, globally averaged. The excessive warming of cold extremes is generally confined to regions where snow and sea ice retreat with global warming. With th

Comment: ‘Knock, Knock: Where is the Evidence for Dangerous Human-Caused Global Warming?’ by Robert M. Carter

Carter (2008) notes that for climate change “sound science [sic] understanding is an essential prerequisite to any meaningful economic analysis”. Unfortunately his paper contains serious and systematic errors and misrepresentations about the causes and potential consequences of climate change, the overall effect of which is to convey an inaccurate and misleading impression of the scientific evidence. Indeed, the overall tone of Carter (2008) is one of a polemic rather than an objective analysis of the facts. An itemisation of all the inaccuracies in Carter (2008) would require a great deal of space, so this paper identifies and corrects some of the most important errors.global warming, human-caused global warming, climate change, economics of climate change, rationalist views on climate change, sceptical views on climate change

Key Scientific Developments Since the IPCC Fourth Assessment Report

Provides an overview of peer-reviewed research published between July 2006 and June 2009 on fossil fuel emissions; ocean acidification; projected sea level rises; rates of ice and permafrost melting and thawing, and the lasting impacts of global warming

A framework for modeling uncertainty in regional climate change

In this study, we present a new modeling framework and a large ensemble of climate projections to investigate the uncertainty in regional climate change over the United States (US) associated with four dimensions of uncertainty. The sources of uncertainty considered in this framework are the emissions projections, global climate system parameters, natural variability and model structural uncertainty. The modeling framework revolves around the Massachusetts Institute of Technology (MIT) Integrated Global System Model (IGSM), an integrated assessment model with an Earth System Model of Intermediate Complexity (EMIC) (with a two-dimensional zonal-mean atmosphere). Regional climate change over the US is obtained through a two-pronged approach. First, we use the IGSM-CAM framework, which links the IGSM to the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM). Second, we use a pattern-scaling method that extends the IGSM zonal mean based on climate change patterns from various climate models. Results show that the range of annual mean temperature changes are mainly driven by policy choices and the range of climate sensitivity considered. Meanwhile, the four sources of uncertainty contribute more equally to end-of-century precipitation changes, with natural variability dominating until 2050. For the set of scenarios used in this study, the choice of policy is the largest driver of uncertainty, defined as the range of warming and changes in precipitation, in future projections of climate change over the US

Potential impact of climate change on improved and unimproved water supplies in Africa

With significant climate change predicted in Africa over the next century, this chapter explores a key question: how will rural water supplies in Africa be affected? Approximately 550 million people in Africa live in rural communities and are reliant on water resources within walking distance of their community for drinking water. Less than half have access to improved sources (generally large diameter wells, springs, or boreholes equipped with handpumps); the majority rely on unimproved sources, such as open water and shallow wells. Major climate modelling uncertainties, combined with rapid socio-economic change, make predicting the future state of African water resources difficult; an appropriate response to climate change is to assume much greater uncertainty in climate and intensification of past climate variability. Based on this assumption the following should be considered: 1. Those relying on unimproved water sources (300 million in rural Africa) are likely to be most affected by climate change because unimproved sources often use highly vulnerable water resources. 2. Improved rural water supplies in Africa are overwhelmingly dependent on groundwater, due to the unreliability of other sources. 3. Climate change is unlikely to lead to continent-wide failure of improved rural water sources that access deeper groundwater (generally over 20 metres below ground surface) through boreholes or deep wells. This is because groundwater-based domestic supply requires little recharge, and the groundwater resources at depth will generally be of sufficient storage capacity to remain a secure water resource. However, a significant minority of people could be affected if the frequency and length of drought increases – particularly those in areas with limited groundwater storage. 4. In most areas, the key determinants of water security will continue to be driven by access to water rather than absolute water availability. Extending access, and ensuring that targeting and technology decisions are informed by an understanding of groundwater conditions, will become increasingly important. 5. Accelerating groundwater development for irrigation could increase food production, raise farm incomes and reduce overall vulnerability. However, ad hoc development could threaten domestic supplies and, in some areas, lead to groundwater depletion. Although climate change will undoubtedly be important in determining future water security, other drivers (such as population growth and rising food demands) are likely to provide greater pressure on rural water supplies

Climate Science: Is it currently designed to answer questions?

For a variety of inter-related cultural, organizational, and political reasons, progress in climate science and the actual solution of scientific problems in this field have moved at a much slower rate than would normally be possible. Not all these factors are unique to climate science, but the heavy influence of politics has served to amplify the role of the other factors. Such factors as the change in the scientific paradigm from a dialectic opposition between theory and observation to an emphasis on simulation and observational programs, the inordinate growth of administration in universities and the consequent increase in importance of grant overhead, and the hierarchical nature of formal scientific organizations are cosidered. This paper will deal with the origin of the cultural changes and with specific examples of the operation and interaction of these factors. In particular, we will show how political bodies act to control scientific institutions, how scientists adjust both data and even theory to accommodate politically correct positions, and how opposition to these positions is disposed of.Comment: 36 pages, no figures. v2: footnotes 16, 19, 20 added, footnote 17 changed, typos corrected. v3: description of John Holdren corrected, expanded discussion of I=PAT formula, typos corrected. v4: The reference to Deming (2005) added in v3 stated that a 1995 email in question was from Jonathan Overpeck. In fact, Deming had left the sender of the email unnamed. The revision v4 now omits the identification of Overpeck. However, the revision v4 now includes a more recent and verifiable reference to a 2005 emai

Ecosystems as climate controllers – biotic feedbacks (a review)

There is good evidence that higher global temperature will promote a rise of green house gas levels, implying a positive feedback which will increase the effect of the anthropogenic emissions on global temperatures. Here we present a review about the results which deal with the possible feedbacks between ecosystems and the climate system. There are a lot of types of feedback which are classified. Some circulation models are compared to each other regarding their role in interactive carbon cycle

ASSESSING THE RISKS OF A FUTURE RAPID LARGE SEA LEVEL RISE: A REVIEW

Our aim is to make an appropriate characterization and interpretation of the risk problem of rapid large sea level rise that reflects the very large uncertainty in present day knowledge concerning this possibility, and that will be useful in informing discussion about risk management approaches. We consider mainly the potential collapse of the West Antarctic ice sheet as the source of such a sea level rise. Our review, characterization and interpretation of the risk makes us conclude that the risk of a rapid large sea level rise is characterized by potentially catastrophic consequences and high epistemic uncertainty; effective risk management must involve highly adaptive management regimes, vulnerability reduction, and prompt development of capabilities for precautionary reduction of climate change forcings.sea level rise, West Antarctic ice sheet, climate change, adaptive management, epistemic uncertainty, risk management arenas, vulnerability

Potential climatic transitions with profound impact on Europe

We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the ‘tipping’ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. <br/